Conventional axial lead inductors consist of a coil of wire wound on an axial leaded form. Such conventional inductors are disclosed in Hill U.S. Pat. No. 2,976,502 and Goldsmith U.S. Pat. No. 3,171,091.
It is considered desirable to provide such inductors with magnetic shielding surrounding the coil winding of the inductor. "Magnetic shielding" is a term of art used to describe a method of enclosing a magnetic field so as to confine its flux, thus preventing interaction with other components or circuits. In the aforementioned Hill patent, a sleeve of finely divided magnetic material is used to enclose a spool and a winding, and serves the function of a magnetic shield. Similarly, in the Goldsmith patent, a layer of high permeability plastic material also functions as a magnetic shield.
It is also considered desirable, in the fabrication of an inductor, to achieve consistent electrical characteristics among the various inductors fabricated. In fact, if variation in the axial and/or radial positioning of the shield of a shielded inductor occurs during the fabrication process, variations in the inductance of the coil and in the degree of shielding will result. This has been considered to be a disadvantageous characteristic of inductors of the prior art.
The following patents are considered to be of background interest relative to the invention disclosed herein: Hill U.S. Pat. No. 2,653,992; Hopkins et al U.S. Pat. No. 2,823,361; Hansen U.S. Pat. No. 3,380,004; Fuller U.S. Pat. No. 3,381,251; Lathouwers et al U.S. Pat. No(s). 3,775,841 and 3,829,806; Kaiserwerth et al U.S. Pat. No. 3,835,370; Sully U.S. Pat. No. 4,170,014; McElheny U.S. Pat. No(s). 4,231,985 and 4,331,946; Hatton U.S. Pat. No. 4,354,310.